Process for the treatment of iron in order to obtain a clean metallic surface



Patented Dec. 7, 1948 PROCESS FOR HIE TREATMENT OF IRON IN ORDER TO OBTAIN A CLEAN METALLIC SURFACE Francisco Ambrosio Ricardo main, Villa Christa, La Rosina, near Lausanne, Switzerland No. Drawing. Application September 13,1945, Serial No. 617,439. In Switzerland February 23,

Claims.

1 Iron and in particular but not exclusively sheet iron is now treated in scouring baths, needing an immersion time of between one to two hours or even more, which treatment must always be followed by others, such as phosphatisation, "parkerisation," bonderisation," etc., designed to give a clean surface suitable for varnishing,

galvanizing or galvanoplastic surfacing.

All these treatments are replaced by the very much more simple process described herein and which is based on the observation that the mixture of a certain proportion of a certain number of acids and salts have the property of cleaning the surface of the iron very rapidly, making it suitable for varnishing, tinning, galvanizing, etc., and at the same time resistant to atmospheric action, on the condition that said surface be totally or partially neutralized by a subsequent alkaline treatment.

According to the present invention, the acid bath is to be composed of by weight 3 to 9 parts of nitric acid, 31 to 33 parts of muriatic acid, 10

to 20 parts of sulphuric acid, 5 to 12 parts of hydrogen sulphide, 1 to 7 parts of sodium acetate and 2 to 9 parts of potassium hydrogen phosphate (Kai-IP04) or potassium ortho phosphate (IQPOi) in 100 parts of water, and the iron to be treated then immersed for 5 to minutes in said bath, its surface at least partially neutralized by immersion in an alkaline bath.

The latter could be composed, for example, by an aqueous solution containing 3 to 10% of caustic soda, 2 to 8% of caustic potash and 5 to 15% of ammonia salts.

Whatever the constitution of the iron surface, whether oxidized or coated with calamine, etc., the piece of iron when withdrawn from the acid bath, in which it must be dipped for no longer a time than mentioned above, but according to its degree of impurity, has an absolute clean, silverlike appearance such as aluminium.

After being neutralized for one or two minutes in an alkaline bath and washed, the iron piece can now be varnished, tinned, galvanized or galvanoplastlcally treated, etc., being understood that enamelling is included under the mention varnish.

Even without one of the above mentioned treatments, the surface obtained would not oxidize and would resist atmospheric action for a very long time. a

This condition could be prolonged indefinely by submitting the treated surface to the action oi a silicate solution varying from 2.5 to 12% of alkalinity at the temperature of to 1009 C.

The time of immersion varies with the volume of the object, but must preferably be such that the object acquires in the bath a temperature of at least 50 0., thus allowing for immediate selfdrying, that is to say without requiring, for example, drying ovens.

The surface of the iron thustreated will remain unaltered for an indefinite period. It will sufflce to wash it with warm water should it at any time require varnishing, tinning, galvanizing etc. If the varnish contains silica and its application requires thermical treatment, then washing in hot water can be suppressed.

Sheet iron treated according to the process of the present invention is suitable for all manufacturing uses within the limits of the above de-v scription, but particularly for replacing tin plate in the manufacture of recipients for the cannin of food, in which case it would be suflicient to surface it with a varnish resisting food sterilizing treatment, each sheet iron until now unsuitable for this purpose being able to be treated without any dimculty in order to have all the necessary qualities.

What I claim is:

.l. A process for the treatment of iron in order to obtain a clean metallic surface, in which the iron to be treated is reacted for -5 to 30 minutes in an acid bath composed of by weight 3 to 9 parts of nitric acid, 31 to 33 parts of muriatic acid, 10 to 20 parts of sulphuric acid, 5 to 12 parts of hydrogen sulphide, 1 to 7 parts of sodium acetate and 2 to 9 parts of a compound from the group consisting of potassium hydrogen phosphate (Kai-IP04) and potassium ortho phosphate (KaPOr) for parts of water, is then withdrawn from said acid bath and immersed in an alkaline bath.

2. A process according to claim 1 in which when withdrawn from the acid bath the iron piece is immersed in an alkaline bath containing 3 to 10% of caustic soda, 2 to 8% of caustic potash, 3 to 15% of ammonia salts and then washed. I

3. A process according to claim- 1 in which when withdrawn from the acid bath the iron piece is immersed for 2 to 6 minutes in an alkaline bath containing 3 to 10% of caustic soda, 2 to 8% of caustic potash, 3 to 15% o! ammonia salts and then washed.

between 2.5 to 12% oi -alkalinity said operation 1 being completed at a temperature of 75 to 100 C.

4. 5. A process according to claim 1 in which when taken out of the alkaline bath the iron piece is immersed in a silicate solution varying between 2.5 to 12% of alkalinity at a temperature of 75 to 100 C. and retained in the silicate solution until temperature of the iron has reached 50 C.

FRANCISCO AMBROBIO RICARDO FRANCHI.

No references cited. 

